A liquid biological sample such as blood is typically taken from a patient using a closed tube with vacuum, as commonly known as vacutainer. To transfer and dispense a volume of the liquid sample from the vacuum tube manually, the sealing cap of the vacuum tube can be removed and a volume of the liquid sample can be taken with a pipette. However, removing the cap of the vacuum tube involves biohazard risks, and shall be avoided whenever it is possible.
Several liquid sample transfer and dispense devices have been developed. One commonly used device in producing blood smear on a microscope slide is known as the Diff-Safe® blood dispenser manufactured by Alpha Scientific Corporation. This dispenser includes a needle in a holder. A sample is taken by penetrating the needle through the sealing cap of a vacuum tube. A droplet of the sample is dispensed on a microscope slide by reversing the vacuum tube and the holder together and placing the holder on the slide, and then pressing on the vacuum tube. The volume of a dispensed droplet is typically in a range from 5 to 30 μl, and the size of the droplet is proportional to the pressure applied on the vacuum tube. Therefore, the dispensed sample volume using such a device varies substantially and lacks accuracy and consistency.
On the other hand, a syringe can also be used for transferring a liquid sample from the vacuum tube. However, it is difficult to dispense an accurate and consistent volume manually with the syringe for a small volume of the sample. Moreover, the internal pressure of filled vacuum tubes varies depending on the extent of filling. This presents a problem when a syringe is used, because the uncontrolled pressure causes variation of the sample volume that is drawn from the filled vacuum tube. Furthermore, the sharp needle of a syringe is not preferred when it comes to operator's safety in handling biological samples.
Therefore, there is a need for an improved dispensing device that overcomes the above mentioned deficiencies.